This invention relates to a four cycle internal combustion engine of the direct injected spark ignited type and more particularly to an improved combustion chamber construction for such an engine.
In the interest of further improving the efficiency and performance of internal combustion engines, direct cylinder injection is increasingly being resorted to. By utilizing direct cylinder injection it is possible to obtain stratification of the mixture at loads less than full load. That can improve not only performance but also fuel efficiency and exhaust emission control. However, in attempting to inject the fuel directly into a open chamber and achieve stratification, it is necessary to insure some way in which a stoichiometric fuel/air mixture is presented at the spark gap at the time the spark plug is fired. Various arrangements have been proposed to achieve this result.
In accordance with one type of methodology, the combustion chamber is formed in part by a recess or bowl formed in the head of piston. The fuel is injected toward this bowl and the induction air is directed so as to cause the fuel to be swept along the surface of the bowl and redirected thereby toward the gap of the spark plug so as to insure that a stoichiometric mixture is present at the time when the spark plug is fired.
Also, in order to insure complete combustion, particularly under high speed high load conditions when a homogenous mixture is provided in the combustion chamber, it is desirable to position the spark plug close to or at the center of the combustion chamber. This means that the bowl or recess must be configured so as to direct the fuel toward the spark plug even under low speed low load conditions.
One structure that has been proposed for this purpose is shown in published Japanese Application Hei 9-144544, published Jun. 3, 1997. This typifies the type of prior art which has been proposed to achieve this result.
The difficulty with this prior art type of construction, however, is that in order to achieve the desired stratification under low speed low load conditions, the bowl in the piston head has had a fairly substantial volume. This means that the compression ratio of the engine is severely limited. This in turn, dictates less then optimal performance.
It is, therefore, a principal object to this invention to provide a combustion chamber configuration wherein direct cylinder fuel injection is possible and wherein the piston head recess is made as small as possible while still achieving the desired results of stratification.
It is a further object to this invention to provide an improved combustion chamber configuration for a direct injection engine having a high compression ratio, a central spark plug position and a bowl in the head of the piston that permits the fuel to be directed toward the gap of the spark plug without significantly adding to the clearance volume of the engine and thus maintaining a high compression ratio.
This invention is adapted to be embodied in an internal combustion engine and more particularly to a combustion chamber therefore. The combustion chamber is defined by a cylinder bore, a cylinder head that closes one end of the cylinder bore and a piston that reciprocates in the cylinder bore. A head of the piston has a generally circular recess formed therein when viewed toward the direction of the axis of the cylinder bore. A fuel injector injects fuel directly into the combustion chamber. An arrangement is provided for causing the fuel flowing from the fuel injector to pass in a circular swirling direction around the axis of the cylinder bore and within the piston head recess. A spark plug is disposed on a side of the piston head recess that is diametrically opposed to the point where the fuel injector injects fuel into the combustion chamber. The piston head recess has a greater depth from a lower surface thereof to the facing surface of the cylinder head on one side of a diametric line extending between the fuel injector and the spark plug, then on the other side of the diametric line. The arrangement for effecting the flow of fuel in the circular swirling direction causes the fuel to flow first into the deeper side of the piston head recess.